The present invention generally relates to an atrial cardiovertor/defibrillator and method for applying cardioverting electrical energy to the atria of a human heart in need of cardioversion. The present invention is more particularly directed to an improved atrial cardiovertor/defibrillator which provides cardioversion therapy corresponding to the relative degree of organization/disorganization of a detected atrial arrhythmia.
Atrial fibrillation is probably the most common cardiac arrhythmia. Although it is not usually a life-threatening arrhythmia, it is associated with strokes thought to be caused by blood clots forming in areas of stagnant blood flow as a result of prolonged atrial fibrillation. In addition, patients afflicted with atrial fibrillation generally experience palpitations of the heart and may even experience dizziness as a result of reduced cardiac output.
Atrial fibrillation occurs suddenly, and many times can only be corrected by an external defibrillator discharging electrical energy to the heart through the skin of the patient. This treatment is commonly referred to as synchronized cardioversion and, as its name implies, involves applying electrical defibrillating energy to the heart in synchronism with a detected R wave of the heart. The treatment is very painful and, unfortunately, most often provides patients only with temporary relief lasting but a few weeks to months.
Drugs are available for reducing the incidence of atrial fibrillation. However, these drugs have many side effects and many patients are resistant to them, which greatly reduces their therapeutic effect.
Implantable atrial defibrillators have been proposed to provide patients suffering from occurrences of atrial fibrillation with relief. Unfortunately, to the detriment of such patients, none of these atrial defibrillators have become a commercial reality. Two such proposed defibrillators, although represented as being implantable, were not fully automatic, require human interaction for cardioverting or defibrillating the heart. Both of these proposed defibrillators require the patient to recognize the symptoms of atrial fibrillation, with one defibrillator requiring a visit to a physician to activate the defibrillator, and the other defibrillator requiring the patient to activate the defibrillator with an external magnet.
An improved atrial defibrillator and lead system which is fully automatic in operation is described in U.S. Pat. No. 5,282,837, which issued on Feb. 1, 1994, for ATRIAL DEFIBRILLATOR AND METHOD, which patent is assigned to the assignee of the present invention and incorporated herein by reference. The defibrillator described in the aforementioned referenced patent automatically detects the presence of an atrial fibrillation episode and applies cardioverting electrical energy to the atria in timed relation to a sensed R wave of the heart. Ventricular pacing is also provided by the described defibrillator.
As can be noted from the above, atrial defibrillators that are currently known detect for the simple presence and absence of atrial fibrillation. If atrial fibrillation is detected, a single therapy regimen is employed. While such devices will provide much needed relief to many patients suffering from atrial fibrillation, further improvements are possible. One such improvement is addressed herein.
It has been observed that atrial activity associated with atrial arrhythmias can vary in organization from highly organized activity to highly disorganized activity. Atrial flutter, for example, is a highly organized atrial arrhythmia. Atrial activity of increasing disorganization, beyond atrial flutter, is generally referred to as atrial fibrillation. Atrial arrhythmias, therefore, encompass a wide range of organization and disorganization from atrial flutter, which is highly organized, to atrial fibrillation, which itself encompasses a wide range of atrial activity organizational characteristics, from what may be referred to as atrial activity of intermediate organization to atrial activity of high disorganization. Recognizing these atrial arrhythmia characteristics, Wells, Jr. et al. in Characterization of trial Fibrillation in Man: Studies Following Open Heart Surgery, Pace, Vol. 1, pp. 426-438, October-December, 1978, type characterized various forms of atrial fibrillation and further reported that the atria, during an arrhythmic episode, can transition between the characterized forms of atrial arrhythmias and can even self-revert to normal sinus rhythm. In addition to the above, it has been more recently learned through research sponsored by the assignee of the present invention that the amount of cardioverting electrical energy required to cardiovert an atrial arrhythmia to return the atria to a normal rhythm increases as the degree of disorganization in atrial activity increases during an arrhythmic episode.
While atrial defibrillators which detect the simple presence and absence of atrial fibrillation (including atrial flutter) and which provide a single intervention regimen if atrial fibrillation is detected will provide needed relief for many patients, these devices for some patients exhibit certain deficiencies. For example, the single intervention regimen can result in a greater amount of electrical energy being applied to the atria than needed to successfully cardiovert the atria. This can submit the patient to a higher degree of potential discomfort than would otherwise be necessary. It can also result in a greater than necessary consumption of battery power which would ultimately shorten the useful life of the cardioverting device. As another example, and at the other end of the organization spectrum, the atrial activity may be so disorganized that the implanted defibrillator is incapable of providing a sufficient amount of energy to cardiovert the atria. Where a single intervention regimen is utilized, therefore, cardioversion would still be attempted with a quantity of cardioverting energy which is less than that required to cardiovert the atria. This would also submit the patient to therapy destined to be ineffective and, hence, therapy which should not be applied, while wasting precious battery power.
The present invention overcomes the previously noted disadvantages in the art by tailoring atrial arrhythmia intervention in accordance with a type classification of the arrhythmia from among a plurality of atrial arrhythmia types. In accordance with one aspect of the present invention, an atrial arrhythmia may be classified as atrial flutter having a high degree of organization, atrial fibrillation having an intermediate degree of organization (type 1), or atrial fibrillation having a high degree of disorganization (type 2). In accordance with another aspect of the present invention, therapy for atrial flutter is provided by atrial pacing or low energy cardioversion and therapy for atrial fibrillation of intermediate organization is provided by medium energy cardioversion. Therapy for atrial fibrillation of high disorganization includes delaying cardioversion for a pre-set time period to permit the atrial activity to potentially transition to atrial fibrillation of intermediate disorganization, whereupon medium energy cardioversion is provided. If the atrial activity does not transition during the pre-set time period, cardioversion of comparatively high energy is provided.
In accordance with another aspect of the present invention, the degree of organization/disorganization of the atrial arrhythmia is determined by atrial cardiac cycle length alone or in combination with atrial cardiac cycle length variability. The atrial cardiac cycle length is determined from the detection of localized activity in one of the atria, such as the right atrium, using a closely spaced bi-polar pair of sensing electrodes.
As will be seen hereinafter, the present invention therefore results in therapy being administered to the patient which is in keeping with the particular type of atrial arrhythmia being experienced by the patient. The present invention therefore provides an improved atrial defibrillator which exhibits significant advantages over prior art atrial defibrillators. Such advantages include a reduction in unnecessary or ineffective cardioversion attempts, less potential discomfort to patients, and the avoidance of unduly shortening the lifetime of an implanted defibrillator.